1. Field of the Invention
The present invention relates to a system for centering a polishing, paint buffing, or paint finishing pad relative to a stiff backing mount. Such pads are typically used to polish, buff, and otherwise finish painted surfaces, such as the painted sheet metal bodies of automotive vehicles.
2. Description of the Prior Art
In finishing hard, painted surfaces the conventional procedure is to buff the surfaces with a soft, cushioning buffing pad using paint finishing, polishing, or buffing compounds of increasing fineness in successive buffing steps. Buffing machines are typically hand held, electrically operated devices that include a generally disk-shaped backing mount for a soft buffing pad. The pad is removably mounted on the backing mount. The backing mount is driven in rotation about a driving axis by an electric motor in the machine, thus turning the pad in rotation as well. The pad is rotated about the driving axis causing the buffing, cutting compound, polish, or glaze to smooth out irregularities in the paint on a painted surface to be finished. Buffing pads of this type are very often used to create a sheer, glossy shine on the surfaces of automotive vehicle bodies that have been painted or repainted, or upon vehicle bodies where oxidation of the paint has occurred and the paint needs to be reconditioned.
A number of different systems have been utilized for securing the soft buffing pad to a backing mount. For many years the standard arrangement was to provide an axially centered opening in the finishing pad and pass the threaded shank of a bolt up through the center of the polishing pad back toward the backing mount. The shank of the bolt was then engaged with a corresponding tapped barrel or sleeve in the backing mount, while the shoulder beneath the head of the bolt clamped the buffing pad against the backing mount.
The head of the bolt was much thinner than the buffing or polishing material which is typically wool fabric or polyurethane foam. A recess in the polishing material was formed at the center of the pad so that the head of the bolt was thereby buried within the polishing material of the pad so as not to contact the painted surface being buffed or polished as the pad rotated. However, individuals operating the buffer or polishing machine can press the buffing pad against the surface being polished with a force sufficient to bring the head of the mounting bolt into contact with the painted surface. Of course, when this occurs there is considerable damage to the paint.
Also, buffing pads with a center mounting bolt could not easily be changed, since each change of a buffing pad required the user to loosen the mounting bolt using a screwdriver or wrench, remove and replace the pad, and retighten the bolt using a screwdriver or wrench. Also, the use of a mounting bolt entailed an additional disadvantage in that if the bolt was not thoroughly tightened, it could come loose during the operation of the buffer or polisher, thus causing damage to the paint finish. As a consequence, other means for fastening paint finishing pads to the stiffer backing mounts were devised.
One particularly popular system for releasably attaching a paint finishing pad to a backing mount is to provide the mounting surface of the pad and the corresponding, facing surface of the backing mount with contact layers bearing mutually engageable hook and loop fabric fasteners. Such hook and loop fasteners form releasable closures having mutually engageable contact surfaces, one of which bears a multiplicity of projecting flexible hooks, typically formed of nylon or other plasticized fabric. The other contact surface bears a flexible, looped pile.
One contact layer, typically the layer bearing the flexible hooks, is attached to the surface of the backing mount that faces the paint finishing pad. The other contact layer, typically the layer bearing the looped pile, is permanently secured to the mounting face of the pad that lies opposite the polishing face. When the contact layers are even lightly pressed together the hooks become releasable engaged in the pile. Such releasable fasteners have been sold for many years under the registered trademark Velcro.RTM. and are described, for example, in U.S. Pat. No. 3,009,235. The attachment system for a polishing head having a detachable pad is described, for example, in U.S. Pat. No. 3,346,904.
By employing a releasable, flexible, fabric hook and loop fastening arrangement, it is unnecessary for any hard object that might damage the surface being finished to be located at the polishing face of the pad. However, one problem which has arisen in elimination of the mounting bolt for fastening the finishing pad to the backing mount is that there is no means for centering the pad relative to the backing mount. As a result, if the pad is placed off center on the backing mount, significant lateral forces are produced in operating the buffer, polisher, or paint finishing machine. These forces must be overcome by the operator, thereby contributing greatly to operator discomfort and fatigue.
One solution which has been attempted to remedy this problem was to configure the mounting surface of the buffing pad such that the outer periphery of the pad surrounding the mounting surface was turned up toward the backing mount to provide an axially extending lip. The backing mount was then enlarged so that the outer, peripheral edge of the backing mount extended all the way to the lip of the flexible backing pad to fit snugly therewithin. Thus, the pad was centered relative to the mount. This system is described in U.S. Pat. No. 5,001,804.
However, configuring the backing mount to fit snugly into the back of the pad also entailed several significant problems. A major disadvantage of the system of U.S. Pat. No. 5,001,804 is that a backing mount can be used only with pads of a specific size. If a larger or smaller pad is to be employed, a corresponding larger or smaller backing mount must also be employed in order for the system to be effective, or even operable. Also, by expanding the size of the backing mount so as to fit within the confines of the flange on the pad backing, both the weight and the expense of the backing mount were greatly increased.